Legal claims defining the scope of protection. Each claim is shown in both the original legal language and a plain English translation.
1. A method, comprising: in a mobile communication terminal, holding a definition of a sub-sampled codebook identifying precoding matrices, which are selected from a master codebook that is made-up of a wideband codebook and a frequency-selective codebook, wherein the definition defines a first subset of the wideband codebook and further defines a second subset of the frequency-selective codebook, wherein the second subset of the frequency-selective codebook is represented using no more than two bits; receiving in the terminal a Multiple-Input Multiple-Output (MIMO) signal; based on the received MIMO signal, selecting from the first subset a single precoding matrix, and selecting from the second subset multiple precoding matrices corresponding to multiple respective spectral sub-bands, for precoding subsequent MIMO signals transmitted to the terminal, and calculating precoding feedback indicating the single precoding matrix selected from the first subset and the multiple precoding matrices selected from the second subset; and transmitting the precoding feedback from the terminal.
A mobile phone performs frequency-selective precoding feedback by using a sub-sampled codebook to reduce overhead. The phone stores a definition of this smaller codebook, which contains precoding matrices selected from a larger "master" codebook. The master codebook consists of a "wideband" component and a "frequency-selective" component. The sub-sampled codebook definition specifies a subset of precoding matrices from the wideband codebook and a subset from the frequency-selective codebook. The frequency-selective subset is small enough to be represented with just two bits. The phone receives a MIMO signal, then selects one precoding matrix from the wideband subset and multiple precoding matrices from the frequency-selective subset (one for each spectral sub-band). Precoding feedback, indicating these selected matrices, is calculated and transmitted from the phone to the base station.
2. The method according to claim 1 , wherein holding the definition comprises defining multiple first subsets and multiple second subsets for multiple respective ranks of the MIMO signal.
The mobile phone described in the previous paragraph uses different sub-sampled codebooks depending on the "rank" (number of data streams) of the MIMO signal. This means the definition of the sub-sampled codebook stores multiple wideband subsets and multiple frequency-selective subsets, each corresponding to a different MIMO rank. Therefore, the precoding matrix selection and feedback process will use the subset combination that matches the current MIMO rank.
3. The method according to claim 2 , wherein defining the second subsets comprises defining each second subset to include only a single precoding matrix for any rank that is higher than a predefined threshold rank.
In the mobile phone from the previous two paragraphs, when using different sub-sampled codebooks for different MIMO ranks, the frequency-selective precoding subset is limited to a single precoding matrix if the MIMO rank is above a certain threshold. So, for higher-rank MIMO signals, only one frequency-selective precoding matrix can be chosen per sub-band from the limited codebook for feedback. This further reduces overhead for higher rank signals.
4. The method according to claim 2 , wherein defining the second subsets comprises defining each second subset to include no more than two precoding matrices for any rank that is higher than a predefined threshold rank.
In the mobile phone from the previous three paragraphs, when using different sub-sampled codebooks for different MIMO ranks, the frequency-selective precoding subset is limited to at most two precoding matrices if the MIMO rank is above a certain threshold. So, for higher-rank MIMO signals, a maximum of two frequency-selective precoding matrices can be chosen per sub-band from the limited codebook for feedback. This still reduces overhead, but allows for slightly more flexibility.
5. The method according to claim 1 , wherein transmitting the precoding feedback comprises sending the precoding feedback over a Physical Uplink Shared Channel (PUSCH).
The mobile phone described in the first paragraph transmits the precoding feedback using the Physical Uplink Shared Channel (PUSCH). The PUSCH is a standard communication channel used for transmitting data from the mobile phone to the base station in LTE and 5G networks.
6. The method according to claim 1 , wherein the wideband codebook and the frequency-selective codebook are each formed of sixteen precoding matrices having first indices {0 . . . 15} and second indices {0 . . . 15}, respectively, wherein the first subset is formed of the precoding matrices having the first indices {0,1,2,...,13,14}, and wherein the second subset is formed of the precoding matrices having the second indices {0,1,2,3} or the precoding matrices having the second indices {0,1,4,5}.
In the mobile phone described in the first paragraph, both the wideband and frequency-selective codebooks in the master codebook contain sixteen precoding matrices, indexed from 0 to 15. The sub-sampled wideband codebook contains the precoding matrices with indices 0 through 14. The sub-sampled frequency-selective codebook contains either the precoding matrices with indices 0, 1, 2, and 3, or the precoding matrices with indices 0, 1, 4, and 5.
7. The method according to claim 1 , wherein holding the definition comprises sub-sampling the master codebook only for ranks of the MIMO signal that are higher than one.
The mobile phone described in the first paragraph only uses the sub-sampled codebook approach for MIMO signals with a rank greater than one. For single-stream (rank 1) MIMO, the full master codebook is used, and no sub-sampling occurs. This focuses the sub-sampling optimization on cases where feedback overhead is most significant.
8. The method according to claim 1 , wherein calculating the feedback comprises calculating multiple Channel Quality Indicators (CQIs) for multiple respective spectral sub-bands, and differentially encoding the multiple CQIs.
In the mobile phone described in the first paragraph, when calculating the precoding feedback, the phone also calculates Channel Quality Indicators (CQIs) for each spectral sub-band. The phone then differentially encodes these CQIs before including them in the feedback. Differential encoding reduces the amount of data required to transmit the CQI information by encoding the difference between consecutive CQI values rather than the absolute values.
9. Apparatus, comprising: a memory, which is configured to hold a definition of a sub-sampled codebook identifying precoding matrices, which are selected from a master codebook that is made-up of a wideband codebook and a frequency-selective codebook, wherein the definition defines a first subset of the wideband codebook and further defines a second subset of the frequency-selective codebook, wherein the second subset of the frequency-selective codebook is represented using no more than two bits; a receiver, which is configured to receive a Multiple-Input Multiple-Output (MIMO) signal; processing circuitry, which is configured to select from the first subset a single precoding matrix, and to select from the second subset multiple precoding matrices corresponding to multiple respective spectral sub-bands, for precoding subsequent MIMO signals transmitted to the receiver, and to calculate precoding feedback indicating the single precoding matrix selected from the first subset and the multiple precoding matrices selected from the second subset; and a transmitter, which is configured to transmit the precoding feedback.
A device comprises a memory, receiver, processor, and transmitter for frequency-selective precoding feedback. The memory stores a sub-sampled codebook definition, identifying precoding matrices from a larger master codebook (wideband and frequency-selective components). The frequency-selective subset uses at most two bits for representation. The receiver gets a MIMO signal. The processor selects a single wideband precoding matrix and multiple frequency-selective precoding matrices (one per sub-band) from the subsets. It calculates precoding feedback indicating these selections. The transmitter sends the feedback.
10. The apparatus according to claim 9 , wherein the memory is configured to hold multiple first subsets and multiple second subsets for multiple respective ranks of the MIMO signal.
The device described in the previous paragraph has a memory that stores multiple wideband subsets and frequency-selective subsets for different MIMO ranks. This enables rank-adaptive sub-sampling of the codebook, optimizing feedback overhead based on the number of data streams being transmitted.
11. The apparatus according to claim 10 , wherein the memory is configured to hold in each second subset only a single precoding matrix for any rank that is higher than a predefined threshold rank.
In the device from the previous two paragraphs, the memory stores frequency-selective subsets containing only a single precoding matrix for ranks above a predefined threshold. This aggressively reduces feedback overhead for higher-rank MIMO signals.
12. The apparatus according to claim 10 , wherein the memory is configured to hold in each second subset no more than two precoding matrices for any rank that is higher than a predefined threshold rank.
In the device from the previous three paragraphs, the memory stores frequency-selective subsets containing no more than two precoding matrices for ranks above a predefined threshold. This offers a trade-off between feedback overhead and precoding flexibility for higher-rank MIMO.
13. The apparatus according to claim 9 , wherein the transmitter is configured to transmit the precoding feedback over a Physical Uplink Shared Channel (PUSCH).
The device from the previous four paragraphs transmits precoding feedback using the Physical Uplink Shared Channel (PUSCH), the standard channel for uplink data transmission.
14. The apparatus according to claim 9 , wherein the wideband codebook and the frequency-selective codebook are each formed of sixteen precoding matrices having first indices {0 . . . 15} and second indices {0 . . . 15}, respectively, wherein the first subset is formed of the precoding matrices having the first indices {0,1,2, . . . ,13,14}, and wherein the second subset is formed of the precoding matrices having the second indices {0,1,2,3} or the precoding matrices having the second indices {0,1,4,5}.
In the device from the previous five paragraphs, the wideband and frequency-selective codebooks each contain sixteen precoding matrices (indexed 0-15). The wideband subset includes matrices with indices 0-14. The frequency-selective subset includes indices 0, 1, 2, 3, or indices 0, 1, 4, 5.
15. The apparatus according to claim 9 , wherein the memory is configured to hold the sub-sampled codebook only for ranks of the MIMO signal that are higher than one.
In the device described in the previous six paragraphs, the memory stores the sub-sampled codebook only for MIMO ranks greater than one, avoiding sub-sampling for single-stream transmissions.
16. The apparatus according to claim 9 , wherein the processing circuitry is configured to calculate multiple Channel Quality Indicators (CQIs) for multiple respective spectral sub-bands and to differentially encode the multiple CQIs, and wherein the transmitter is configured to transmit the differentially-encoded CQIs in the feedback.
In the device described in the previous seven paragraphs, the processing circuitry calculates CQIs for each spectral sub-band, differentially encodes them, and includes the encoded CQIs in the feedback transmitted by the transmitter.
17. A mobile communication terminal comprising the apparatus of claim 9 .
A mobile communication terminal incorporates the device from the previous eight paragraphs, implementing frequency-selective precoding with sub-sampled codebooks to reduce feedback overhead.
18. A chipset for processing signals in a mobile communication terminal, comprising the apparatus of claim 9 .
A chipset for mobile communication terminals incorporates the device from the previous nine paragraphs, providing the capability for frequency-selective precoding with sub-sampled codebooks.
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December 30, 2014
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